Frequently, combi rolls include two or more roll rings, which are kept separated by intermediate spacer rings, the entire set of rings being kept fixed on the shaft by way of, on one hand, a fixed stop ring, e.g., a shoulder of the roll shaft, and, on the other hand, a lock nut that via an internal thread may be tightened on a male thread of the shaft. Furthermore, between the lock nut and the set of roll rings, spring devices as well as additional spacer rings may be present.
In many cases, the roll rings are manufactured from cemented carbide, while the intermediate spacer rings are manufactured from a softer or more ductile material, preferably steel or cast iron. Considerable torque should be transmitted to the roll rings from the roll shaft. When the roll rings are made of solely cemented carbide, this usually takes place by an axial (cylindrical) train of forces from the lock nut to the fixed stop ring via the contact surfaces between the individual rings. More precisely, the torque is transmitted from the individual ring to an adjacent ring by a friction action in the interfaces, where an end surface of a ring is pressed against a co-operating end surface of the adjacent ring. In order to fulfil this task throughout the train of forces, the individual friction joints between the rings have to be powerful, i.e., be able to transfer torque without the rings slipping in relation to each other.
In previously known combi rolls (see, for instance, U.S. Pat. No. 5,735,788 and U.S. Pat. No. 6,685,611) the roll rings as well as the spacer rings are formed with end surfaces extending radially all the way from the inside to the outside, i.e., from the envelope surface of the roll shaft to the external cylinder surface of the individual ring. However, this fact has turned out to be detrimental for the ability of the friction joints to transmit a large torque between the rings. Thus, the described design results in the transmission of force in a zone situated about halfway between the inside and the outside of the spacer ring, i.e., as close to the envelope surface and the center axis of the roll shaft, respectively, as possible. Furthermore, the surface pressure in the interfaces between the contact surfaces becomes relatively low because the contact surfaces are comparatively large. For these reasons, it may happen that the rings slip in relation to each other, something which in turn may lead to production interruptions and in the worst case, roll breakdowns.